JP2008187259A - Radio communication method, and radio communication terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication method and a radio communication terminal that are not mounted with a GPS receiver, can be made compact and inexpensive, eliminate the need to revise an existent communication protocol, are free of a rise in current consumption, can positively and efficiently select a base station in a moving direction during movement, and can make a smooth handover and perform the saving of a battery. <P>SOLUTION: Relative distance differences by a plurality of base stations are calculated based upon periodic reception timings of notice information channel bursts radiated synchronously from the base stations 1A to 1F, an estimated moving speed of a radio communication terminal is calculated based upon the relative distance differences by the base stations, and when the estimated moving speed is larger than a predetermined threshold, a base station in the moving direction of the radio communication terminal is selected based upon the relative distance differences by the base stations. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication method and a wireless communication terminal for performing wireless communication with a base station by a TDD (Time Division Duplex) method.

  For example, a PHS system is known as a wireless communication system that employs the TDD scheme. The PHS system is standardized by ARIB STD 28 and adopts a TDMA / TDD digital wireless communication system in which multiple access is performed by a TDMA (Time Division Multiple Access) system.

  In the PHS system, the upper base station receives time synchronization (so-called GPS synchronization) by receiving GPS (Global Positioning System) radio waves, and the lower base station performs time synchronization based on broadcast information from the GPS synchronized base station. It is devised so that the TDMA / TDD frames of all the base stations are synchronized by synchronizing (so-called air synchronization). A radio communication terminal of the PHS system monitors a broadcast information channel burst transmitted by a base station for a certain period, and normally transmits a broadcast information burst having the strongest RSS1 (Received Signal Strength Indicator). The base station is selected as a base station to be awaited.

  In the PHS system, logical slots on TDMA / TDD for transmitting broadcast information channel bursts are determined, and base stations in the vicinity distribute transmission timing for each frame so that broadcast information channel bursts do not collide. Yes. Also, in a radio communication terminal, when going away from the currently selected base station, the RSSI from the base station deteriorates, so a base station selection holding threshold is set, and the RSSI deteriorates beyond that threshold. In this case, the broadcast information channel burst transmitted by the neighboring base station is monitored again for a certain period, and usually the control is performed to switch the selection to the base station transmitting the broadcast information channel burst having the strongest RSSI. I am doing so. This operation is a handover operation during communication.

  Since the PHS system is mainly for voice calls, in the wireless communication terminal, the base station selection holding threshold is set low so that the connection with the base station once selected is persistently held.

  On the other hand, recently, a data communication system that supports a plurality of modulation classes has been put into practical use. In such a system, since a modulation class having a higher throughput is used, it is preferable to actively search for a base station having a better radio wave condition. That is, a modulation scheme having a high throughput usually requires a high reception level because it requires a high signal-to-interference plus noise ratio (SINR). Therefore, in such a wireless communication terminal, for example, in a 10-second cycle, the broadcast information channel burst transmitted by the base station is monitored for a certain period, and a base station with better conditions than the currently waiting base station is searched for. It is preferable to switch stations.

  By the way, when a wireless communication terminal is moved, if handover is performed simply by selecting a base station (substantially close base station) having a large RSSI, the number of handovers increases as the movement becomes faster. For this reason, for example, when performing real-time communication such as VoIP, instantaneous interruption of communication at the time of handover frequently occurs, and communication quality is extremely inferior.

  As a method for preventing this, it is conceivable to positively select a base station in the direction of travel when moving. In this way, it is expected that the area of the destination base station can be traversed more than when selecting a base station in a position that is not in the traveling direction, so it can stay at the destination base station for a longer time, As a result, since the number of handovers can be reduced, the number of instantaneous interruptions of communication due to handover can be reduced, and there is an advantage that good communication quality can be maintained.

  As such a base station selection method, for example, a GPS receiver is mounted on a wireless communication terminal, and storage means for storing the switching position of the base station in advance is provided, and position information received by the GPS receiver is stored in the storage means. There is known one in which a base station is switched when a switching position is reached (see, for example, Patent Document 1).

  As another base station selection method, for example, a GPS receiver is mounted on a wireless communication terminal to acquire position information, and the position information is sequentially transmitted to the selected base station. Detects the traveling direction of a communication terminal, and exists in a predetermined fan-shaped area that spreads in the traveling direction around the current location of the wireless communication terminal from the base station information registered in the neighbor set of the wireless communication terminal It is known that a base station located in the traveling direction can be preferentially selected as a base station to be used next by extracting a base station to be notified (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 10-341470 Japanese Patent Laid-Open No. 2002-159039

  However, in the base station selection methods described in Patent Documents 1 and 2, since the GPS receiver is mounted on the wireless communication terminal, there is a concern that the wireless communication terminal may be increased in cost and size. . In addition, in the base station selection method described in Patent Document 2, it is necessary to extract and notify a base station existing in a predetermined fan-shaped area that spreads in the traveling direction around the current location of the wireless communication terminal Therefore, it is effective when standardization is possible, but in a system that has already started operation, protocol revision is necessary, which is not realistic.

  In a wireless communication terminal, a base station with a good radio wave condition is selected by following the movement by shortening the monitoring period of the broadcast information channel burst transmitted by a neighboring base station without detecting its position. However, there is a concern that the current consumption increases and the battery life becomes worse.

  Therefore, an object of the present invention made in view of such circumstances is to be able to be small and inexpensive without mounting a GPS receiver, and without revising an existing communication protocol or causing an increase in current consumption. Another object of the present invention is to provide a radio communication method and a radio communication terminal capable of positively and efficiently selecting a base station in the direction of travel when moving and performing smooth handover and battery saving.

The invention of a wireless communication method according to claim 1 that achieves the above object is a wireless communication method in a wireless communication terminal that performs wireless communication with a base station by a time division duplex method,
A first step of periodically receiving broadcast information channel bursts radiated synchronously from a plurality of base stations;
A second step of calculating a relative distance difference for each base station with respect to the wireless communication terminal based on reception timing of sequential broadcast information channel bursts for each base station received in the first step;
A third step of calculating an estimated moving speed of the wireless communication terminal based on the relative distance difference for each base station calculated in the second step;
Based on a comparison result between the estimated moving speed calculated in the third step and a predetermined threshold, and when the estimated moving speed is equal to or greater than the threshold, based on the relative distance difference for each base station calculated in the second step. A fourth step of selecting a base station in the direction of travel of the wireless communication terminal,
It is characterized by including.

The invention according to claim 2 is the wireless communication method according to claim 1,
The third step includes
The estimated moving speed is calculated based on the maximum absolute value among the relative distance differences for each base station calculated in the second step.

The invention according to claim 3 is the wireless communication method according to claim 1 or 2,
The fourth step further includes:
Calculating a relative speed for each base station with respect to the wireless communication terminal based on the relative distance difference for each base station calculated in the second step;
Based on the calculated relative speed for each base station and the estimated moving speed calculated in the third step, an angle for each base station indicating the direction in which each base station is located with respect to the wireless communication terminal is calculated. Steps,
Based on the reception timing of the broadcast information channel burst for each base station, calculating the relative distance difference of the other base station with respect to the base station currently selected by the wireless communication terminal,
In accordance with the calculated angle for each base station and the calculated relative distance difference between other base stations with respect to the currently selected base station, the angle set in advance as the traveling direction in the received signal strength for each base station In a predetermined angle region including a positive correction value that is set so as to increase as the moving direction component increases and further away from the currently selected base station, it is opposite to the moving direction direction. In a predetermined angle region including a direction angle, a step of adding a negative correction value set so as to be smaller as the opposite direction component is larger and to be farther away from the currently selected base station; and
And the base station having the maximum received signal strength among the received signal strengths for each base station to which the correction value is added is selected as a base station in the traveling direction of the wireless communication terminal. It is.

The invention according to claim 4 is the wireless communication method according to any one of claims 1 to 3,
The reception period of the next broadcast information channel burst in the first step is controlled according to the estimated moving speed calculated in the third step.

The invention according to claim 5 is the wireless communication method according to claim 4,
The reception period is controlled so as to become shorter as the estimated moving speed becomes faster.

Further, the invention of a wireless communication terminal according to claim 6 that achieves the above object is a wireless communication terminal that performs wireless communication with a base station by a time division duplex method.
Receiving means for periodically receiving broadcast information channel bursts radiated synchronously from a plurality of base stations;
Relative distance difference calculating means for calculating a relative distance difference for each base station with respect to the wireless communication terminal based on reception timing of sequential broadcast information channel bursts for each base station received by the receiving means;
Based on the relative distance difference for each base station calculated by the relative distance difference calculating means, estimated moving speed calculating means for calculating the estimated moving speed of the wireless communication terminal;
Based on the comparison result between the estimated moving speed calculated by the estimated moving speed calculating means and a predetermined threshold, when the estimated moving speed is equal to or greater than the threshold, each base station calculated by the relative distance difference calculating means Base station selection means for selecting a base station in the traveling direction of movement of the wireless communication terminal based on the relative distance difference;
It is characterized by having.

  According to the present invention, the relative distance difference for each base station is calculated based on the periodic reception timing of broadcast information channel bursts radiated synchronously from a plurality of base stations, and the relative distance difference for each base station is calculated. Based on a relative distance difference for each base station, when the estimated moving speed of the wireless communication terminal is calculated based on the relative distance difference for each base station, Since it is selected, it is possible to reduce the size and cost without mounting a GPS receiver, and without changing the existing communication protocol or incurring an increase in current consumption. A certain base station can be positively and efficiently selected, and smooth handover and battery saving can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic configuration of a wireless communication system using a wireless communication terminal according to an embodiment of the present invention. In FIG. 1, a plurality of base stations 1A, 1B, 1C,... Are connected to the Internet 3 via a PDSN (Packet Date Serving Node) 2, and a SIP (Session Initiation Protocol) telephone 4 is connected to the Internet 3. And the SIP server 5 are connected. The wireless communication terminal 10 communicates with the SIP telephone 4 connected to the Internet 3 through one of the base stations 1A, 1B, 1C,. In the following description, when the base station is not specified, it is simply indicated as the base station 1. Here, a TDMA / TDD digital wireless communication system is adopted as a wireless communication system between the wireless communication terminal 10 and the base station 1.

  FIG. 2 shows an example of a frame configuration according to the TDMA / TDD digital radio communication system. Here, one frame is 5 msec, and an uplink frame that is a transmission frame of the radio communication terminal 10 and a downlink frame that is a transmission frame of the base station 1 each have three slots, slot 0 to slot 2. One slot of the uplink is 545 μsec, and one slot of the downlink is 1090 μsec. Also, a guard time of 10 μsec is provided between the uplink frame and the downlink frame, and a guard time of 85 μsec is provided between the downlink frame and the uplink frame of the next frame. Yes.

  In the downlink frame, the first slot 0 is used as a broadcast information channel, and is used as shown in FIG. 3, for example. In FIG. 3, 16 frames are defined as one super frame (80 msec), and broadcast information channel bursts (B0 to B7) of one base station 1 are allocated to the odd frames (k, k + 2, k + 4,...). , Divided into 8 groups in total. Therefore, in this system, a total of eight base stations 1 can exist in the same region. In the superframe shown in FIG. 3, for example, a configuration information request channel burst (D) is assigned to even frames (k + 1, k + 3, k + 5,...).

  The broadcast information channel has, for example, a symbol coding format as shown in FIG. That is, the broadcast information channel carries information of 545 symbols (1 symbol: 2 μsec) as a whole, and is used for the 5 symbol inter-slot guard time G from the head, the extended guard time EG of 43 symbols, and the transient response of 2 symbols. Ramp time R, 32 symbol preamble PR, 32 symbol unique word UW, 381 symbol broadcast information element symbol BI, 2 symbol transient response ramp time R, 43 symbol extended guard time EG, and last 5 symbols It has an inter-slot guard time G.

  As shown in FIG. 4, the broadcast information channel has an extended guard time EG before and after, so that it becomes smaller than the downlink slot. Therefore, while synchronizing with the broadcast information channel of an arbitrary base station 1, other broadcast information channels of the base station 1 (with different distances from the radio communication terminal 10) are within the range of the reception window of the same downlink slot. Reception is possible.

Here, if the radio propagation speed is 3 * 10 ⁸ m / sec, the relative distance from the radio communication terminal 10 is 300 m for 1 μsec. Therefore, when the head of the downlink slot 0 is adjusted at the guard time G of an arbitrary base station 1, the relative distance from the wireless communication terminal 10 to the target base station 1 is 0. .3 km * (43 * 2 μsec) = 28.5 km away, the broadcast information channel transmitted by another base station 1 can be received in terms of timing.

  Hereinafter, a case where the wireless communication terminal 10 moves on a map as shown in FIG. 5 will be described as an example.

  In FIG. 5, it is assumed that the wireless communication terminal 10 captures the radio wave of the base station 1A for the first time at the point a and knows that communication is possible. Naturally, at the point a, the radio communication terminal 10 can only observe the radio waves of the base station 1A, so the base station 1A is selected.

  Thereafter, when the wireless communication terminal 10 moves to the point b, it is assumed that the RSSI of the radio wave transmitted by the base station 1A has weakened and reselects the base station. At this time, it is assumed that the point b is a downtown area and the four base stations 1A, 1B, 1C, 1D can be recognized, but all are weak broadcast information channels.

  In this case, the conventional wireless communication terminal selects the nearest base station 1B having the strongest RSSI among them. Similarly, when the conventional wireless communication terminal recognizes that the RSSI of the radio wave transmitted by the base station 1B has weakened when moving to the point c, and reselects the base station, In c, the nearest base station 1C having the strongest RSSI is selected. Similarly, in point d, the nearest base station 1E having the strongest RSSI is selected, and in point e, the nearest RSSI has the strongest RSSI. The neighboring base station 1F is selected, and the base station ahead in the moving direction is not positively selected.

  In radio communication terminal 10 according to the present embodiment, broadcast information channel bursts radiated synchronously from a plurality of base stations are periodically received, and the relative distance difference for each base station based on the sequential reception timing And the estimated moving speed of the wireless communication terminal 10 is calculated based on the relative distance difference for each base station. If the estimated moving speed is equal to or greater than a predetermined threshold, the estimated moving speed is based on the relative distance difference for each base station. The base station in the direction of travel of the wireless communication terminal 10 is selected. Thus, for example, in FIG. 5, when the base station is reselected after passing the point b, the base station 1D located in the moving direction among the four recognized base stations 1A, 1B, 1C, 1D is selected. When selecting and then reselecting the base station after passing through the point d, the base station 1F located in the moving direction is selected from the three recognized base stations 1D, 1E, and 1F.

  FIG. 6 is a functional block diagram illustrating a configuration of a main part of the wireless communication terminal 10 according to the embodiment of the present invention. The wireless communication terminal 10 includes an antenna 11, an RF unit 12, a demodulator 13, an AFC (Automatic Frequency Controller) unit 14, a UW detector 15, a decoder 16, a baseband control unit 17, a CODEC (codec) 18, a speaker 19, A configuration of a conventional wireless communication terminal having a microphone 20, an encoder 21, and a modulator 22 is added with an edge detection unit 25, an edge position storage register 26, and a timer unit 27 that manages the edge detection unit 25.

  Radio communication terminal 10 of the present embodiment performs a reception operation on the carrier for a sufficient period including broadcast information channel bursts B0 to B7 shown in FIG. In this reception operation, the reception signal received by the antenna 11 is converted into IF data by the RF unit 12 and supplied to the demodulator 13, where it is converted into an information string for each symbol and supplied to the UW detector 15. The

  The UW detector 15 sequentially monitors the information sequence for each symbol supplied from the demodulator 13. When the UW detector 15 recognizes the information sequence that matches the UW, the UW detector 15 stores the position thereof, and the broadcast information element information sequence ( Assuming that there is BI), the symbol information string is passed to the decoder 16. The decoder 16 analyzes the symbol information sequence from the UW detector 15 to identify the base station based on the broadcast information element information sequence (BI), and also reports the RSSI of the broadcast information channel burst transmitted by each base station. The timing is collected and supplied to the baseband controller 17.

  In the voice call after the base station is selected, the received voice signal decoded by the decoder 16 and supplied to the baseband control unit 17 is decoded by the CODEC 18 and sent to the speaker 19 as an analog signal, as in the conventional wireless communication terminal. Is output. An audio signal received by the microphone 20 is encoded into a digital signal by the CODEC 18 and then radiated from the antenna 11 via the baseband control unit 17, the decoder 21, the modulator 22, and the RF unit 12. The frequency signal required for transmission / reception in the RF unit 12 and the frequency signal required for demodulation in the demodulator 13 are supplied from the AFC unit 14 under the control of the baseband control unit 17.

  Next, operations of the edge detection unit 25, the edge position storage register 26, and the timer unit 27, which are characteristic configurations of the wireless communication terminal 10 in the present embodiment, will be described.

  FIG. 7 shows a relative movement situation of the base stations 1A to 1D with respect to the wireless communication terminal 10 according to the reception timing of the broadcast information channel burst at the point b in FIG. That is, since the wireless communication terminal 10 is on a train, when the train is moving upward at a speed v, assuming that the relative speed of the train is zero, the entire drawing excluding the train is relatively downward. It is synonymous with moving at speed v. Therefore, at sequential base station monitor timings, the base stations 1A to 1D appear to move at the relative speeds a to d shown in FIG. 7 with respect to the radio communication terminal 10 in the train.

  Based on the output of the demodulator 13, the edge detection unit 25 detects the rising edge of the broadcast information channel burst at the ramp time (R) when receiving the broadcast information channel of each base station, and the timer unit 27 at the time of detection. The counter value is captured and stored in the edge position storage register 26. The timer unit 27 includes a free-run timer that circulates at 5000 μsec (5 msec) in synchronization with the AFC unit 14.

  Here, the free-run timer period of the timer unit 27 is made to coincide with the TDMA / TDD frame period adopted by the wireless communication method shown in FIG. However, this free-run timer period is generated by the radio communication terminal 10 and is basically asynchronous with the TDMA / TDD frame period based on the burst transmitted by the base station. For this reason, it shifts due to Doppler fading due to movement or a difference in clock accuracy, and it is uncertain at which position of the free-run timer the broadcast information channel burst of each base station is recognized.

  FIG. 8 is a timing chart showing the edge positions of the broadcast information channel bursts of the base stations 1A to 1D obtained at the reception timing at the point b, and FIG. 9 is obtained at the next reception timing after 10 seconds from FIG. It is a timing diagram which shows the edge position of the alerting | reporting information channel burst of base station 1A-1D which was made. Note that the numbers in the figure are the count accuracy of the timer unit 27, here 1/6 μsec.

  The selected base station at the point b is the base station 1A. By using the timing offset of the broadcast information channel bursts of the base stations 1A to 1D available at this time, the distance relationship between the base stations with respect to the wireless communication terminal 10 Can know. For example, at point b, it can be seen that the base station 1A is closest to the radio communication terminal 10 and the base station 1D is furthest from the radio communication terminal 10, and the relative distance is ((459-432) / 6) *. It can be seen that 0.3 = 1.35 (Km).

  Further, the baseband controller 17 performs a required calculation using data obtained from the edge position storage register 26 by scanning the base station at the broadcast information channel burst reception cycle (here, 10 sec cycle). The relative movement status of each base station can be estimated. Table 1 shows the relative movement status of the base stations 1A to 1D with respect to the wireless communication terminal 10 obtained from the numerical values on the timing charts of FIGS.

  As described above, based on the change in the edge position at the reception timing of sequential broadcast information channel bursts, the relative speed with respect to the radio communication terminal 10 for each base station can be obtained, and each base with any base station as a reference A relative distance difference between the station and the wireless communication terminal 10 can be obtained.

  In addition, since the moving speed v of the radio communication terminal 10 cannot be directly known, an offset difference Doffset that is a relative distance difference for each base station with respect to the radio communication terminal 10 obtained from sequential reception timings of broadcast information channel bursts. The relative speed calculated based on the largest absolute value | Doffset | is adopted as the estimated moving speed v ′ of the wireless communication terminal 10.

  In the present embodiment, when the estimated moving speed v ′ does not reach the threshold value, it means that the moving speed of the radio communication terminal 10 is slow or that the base station is not in the traveling direction or the opposite side of the traveling direction. Therefore, in this case, the reception cycle of the broadcast information channel burst is lengthened or the current reception cycle is maintained, for example, to the base station transmitting the broadcast information burst having the strongest RSSI as in the conventional case. Control for switching the selection is performed, and when the estimated moving speed v ′ is equal to or higher than the threshold value, control is performed so as to positively select a base station in the moving direction.

  Here, the threshold value to be compared with the estimated moving speed v ′ is, as shown in FIG. 5, in a case where the main purpose is to place the base station on the train line and capture the forward base station, It can be set based on the cruise speed of the train. For example, when the cruising speed of the train is 150 km / h, almost half of the speed is set as the threshold value. In this way, when the estimated moving speed v ′ is a low speed of less than 20 m / sec, or when the base station cannot be placed beside the track, improper operation due to the estimated error of the estimated moving speed v ′ is suppressed. Can do.

  In this way, as shown in FIG. 10, when the wireless communication terminal 10 is moving at a speed v exceeding the threshold in the direction of angle 0 (upward in the drawing), it exists in the traveling direction area A near the angle 0. The base station to be actively selected is selected, and conversely, control is performed so that the base station existing in the opposite direction region B near the angle ± π with respect to the traveling direction is actively released.

  For example, in FIG. 5, four base stations 1A to 1D are identified at a point b, and after that, 5 seconds have elapsed since the base station scan was performed at the reception timing of the next broadcast information channel burst, that is, from the point b. It is assumed that at the time point after 15 seconds, the base station 1A, which is the selected base station, recognizes a decrease in RSSI and attempts to select a base station. In this case, the estimated moving speed v ′ obtained from the base station scan data received at the reception timing of the immediately previous broadcast information channel burst exceeds 20 m / sec, and the currently selected base station is moving away. If detected, control is performed so as to positively select a base station existing in the traveling direction area A.

  For this reason, first, it is assumed that the base station having the maximum absolute value | Doffset | of the offset difference is on the extension line in the traveling direction. That is, when the offset difference Doffset of the base station that is the maximum | Doffset | is positive, it is located in the direction of angle 0 for the radio communication terminal 10, and conversely, for the radio communication terminal 10, it is negative. Assume that it is located in the direction of angle ± π.

Here, when the base station x is at infinity, the angle ω seen from the radio communication terminal 10 of the base station x is the relative speed v [x] of the base station x and the estimated moving speed v of the radio communication terminal 10. From the speed ratio with ′,
ω = cos ⁻¹ (v [x] / v ′)
It can ask for. In this equation, since a negative number does not appear, it is impossible to determine whether the base station x is located on the right or the left with respect to the traveling direction. Since the position of the left and right with respect to the traveling direction is not a problem and the angle ω of the base station x viewed from the wireless communication terminal 10 does not require so high accuracy, the angle ω is, for example, Calculate according to Table 2.

  Further, the estimated moving speed v ′ of the radio communication terminal 10 is the relative speed of the base station 1D having the largest absolute value | Doffset | of the offset difference, and therefore v ′ = 45 m / sec.

  From the above values, the results shown in Table 3 are obtained as the relative speed of each base station, the estimated moving speed ratio (θ), and the angle ω with respect to the traveling direction in 10 seconds at the point b.

  When each base station is mapped according to the angle ω of each base station calculated as described above and the relative distance difference h from the selected base station, it is as shown in FIG.

  Furthermore, in the present embodiment, as shown in FIG. 12, the RSSI corresponding to the angle ω and the relative distance difference h from the selected base station is selected so as to positively select a base station existing in the traveling direction area A. The correction values are set in advance, and these correction values are added to the measured actual RSSIs to obtain corrected RSSIs as shown in Table 4. Based on the comparison of the corrected RSSIs, A strong RSSI base station is selected. Here, the RSSI correction value is larger as the moving direction component increases in a predetermined angle region (0 ± 1 / 6π in FIG. 12) including an angle set in advance as the moving direction, and is currently selected. Set to a positive correction value that increases as the distance from the base station increases. In a predetermined angle region including an angle opposite to the moving direction (π ± 1 / 2π in FIG. 12), the opposite direction component is large. The negative correction value is set so as to be smaller and smaller as the distance from the currently selected base station increases.

  As a result, when 15 seconds have elapsed from the point b, not the base station 1B but the base station 1D located in the direction of travel of the wireless communication terminal 10 is selected. In addition, the base station 1A is extremely difficult to select because of extremely bad conditions.

  Therefore, in FIG. 6, the receiving means for periodically receiving the broadcast information channel burst is configured to include the antenna 11, the RF unit 12, and the demodulator 13, and calculate the relative distance difference for calculating the relative distance difference for each base station. The means includes a baseband control unit 17, an edge detection unit 25, an edge position storage register 26, and a timer unit 27, and an estimated movement speed calculation unit that calculates an estimated movement speed of the wireless communication terminal 10, and an estimated movement speed The base station selection means for selecting a base station in the direction of travel of the wireless communication terminal 10 when the value is equal to or greater than the threshold is configured to include the baseband control unit 17.

  As described above, according to the present embodiment, as shown in FIG. 6, the edge detector 25, the edge position storage register 26, In addition, with a small and inexpensive configuration that adds a timer unit 27 that manages the edge detection unit 25, the base station selection algorithm is switched by estimating the movement status of the terminal from the delay width on the TDD frame of a plurality of received broadcast bursts. Since it did in this way, the base station located in the movement advancing direction can be selected efficiently and rapidly, and the radio | wireless communication terminal 10 which can perform a smooth handover and battery saving can be obtained. In addition, since it is not necessary to revise the existing communication protocol, it can be effectively applied to an existing system (for example, a PHS system or an iBurst (registered trademark) system), and a base station in the moving direction is positively selected. As a result, the number of handovers can be reduced, and improvement in call quality can be expected. In addition, in a wireless communication system that wirelessly transmits an IP packet transmission path, the IP-ID of an RTP / UDP / IP packet intended for ROHC compression is changed according to the base station located in the moving direction of the terminal. Thus, an optimal compression rate can be obtained in ROHC compression. Furthermore, when the terminal is stopped, the reception period of the broadcast information channel burst is lengthened, so that the current consumption can be reduced and the battery can last longer.

  In addition, this invention is not limited only to the said embodiment, Many deformation | transformation or a change is possible. For example, the broadcast information channel burst reception period can be set according to the moving speed of the terminal. For example, for the estimated moving speed | v ′ |, a high threshold value vrefH and a lower threshold value vrefL are provided. When the estimated moving speed | v ′ | is between the threshold value vrefH and the threshold value vrefL, If the estimated movement speed | v ′ | exceeds the threshold value vrefH, the monitor cycle is set to a shorter value (for example, 5 seconds). If the estimated movement speed | v ′ | Set longer (for example, 20 sec). In this way, it is possible to follow the change in the situation of the base station more efficiently while suppressing battery consumption efficiently. When the estimated moving speed | v ′ | is low, the synchronization deviation with the base station is dominated by the difference in clock accuracy between the reference clock of the wireless communication terminal and the burst transmitted by the base station. Although the change in the burst position due to the movement of the distance is not dominant, in such a case, there is no problem because the synchronization with the base station is maintained even if the monitoring period is extended.

  In addition, since the broadcast information channel burst is periodically monitored, the data communication main system that supports a plurality of modulation classes is more conditional than the base station that is currently waiting based on RSSI for each broadcast information channel burst reception. It is also possible to search for a good base station and switch the standby base station.

It is a figure which shows schematic structure of the radio | wireless communications system using the radio | wireless communication terminal which concerns on one embodiment of this invention. It is a figure which shows an example of the frame structure by a TDMA / TDD digital wireless communication system. It is a figure which shows an example of the super-frame structure of an alerting | reporting information channel. It is a figure which shows an example of the symbol coding format of a broadcast information channel. It is a figure for demonstrating selection operation | movement of the base station in case a radio | wireless communication terminal train-moves on a map. It is a functional block diagram which shows the structure of the principal part of the radio | wireless communication terminal which concerns on one embodiment of this invention. It is a figure which shows the relative movement condition with respect to the radio | wireless communication terminal of each base station in the point b of FIG. FIG. 6 is a timing chart showing an edge position of a broadcast information channel burst of each base station obtained at a reception timing at point b in FIG. 5. FIG. 9 is a timing chart showing an edge position of a broadcast information channel burst of each base station obtained at a reception timing next to the reception timing of FIG. 8. It is a figure for demonstrating the base station selection operation | movement at the time of a movement. It is a figure which shows angle (omega) of each base station at the time of a movement, and the relative distance difference h with a selection base station. It is a figure which shows the correction value of RSSI according to angle (omega) of each base station at the time of a movement, and relative distance difference h with a selection base station.

Explanation of symbols

1A, 1B, 1C Base station 2 PDSN
3 Internet 4 SIP telephone 5 SIP server 10 Wireless communication terminal 11 Antenna 12 RF unit 13 Demodulator 14 AFC unit 15 UW detector 16 Decoder 17 Baseband control unit 18 CODEC
DESCRIPTION OF SYMBOLS 19 Speaker 20 Microphone 21 Encoder 22 Modulator 25 Edge detection part 26 Edge position memory register 27 Timer part

Claims (6)

A wireless communication method in a wireless communication terminal that performs wireless communication with a base station using a time division duplex method,
A first step of periodically receiving broadcast information channel bursts radiated synchronously from a plurality of base stations;
A second step of calculating a relative distance difference for each base station with respect to the wireless communication terminal based on reception timing of sequential broadcast information channel bursts for each base station received in the first step;
A third step of calculating an estimated moving speed of the wireless communication terminal based on the relative distance difference for each base station calculated in the second step;
Based on a comparison result between the estimated moving speed calculated in the third step and a predetermined threshold, and when the estimated moving speed is equal to or greater than the threshold, based on the relative distance difference for each base station calculated in the second step. A fourth step of selecting a base station in the direction of travel of the wireless communication terminal,
A wireless communication method comprising: The third step includes
The wireless communication method according to claim 1, wherein the estimated moving speed is calculated based on a maximum absolute value among the relative distance differences for each base station calculated in the second step. The fourth step further includes:
Calculating a relative speed for each base station with respect to the wireless communication terminal based on the relative distance difference for each base station calculated in the second step;
Based on the calculated relative speed for each base station and the estimated moving speed calculated in the third step, an angle for each base station indicating the direction in which each base station is located with respect to the wireless communication terminal is calculated. Steps,
Based on the reception timing of the broadcast information channel burst for each base station, calculating the relative distance difference of the other base station with respect to the base station currently selected by the wireless communication terminal,
In accordance with the calculated angle for each base station and the calculated relative distance difference between other base stations with respect to the currently selected base station, the angle set in advance as the traveling direction in the received signal strength for each base station In a predetermined angle region including a positive correction value that is set so as to increase as the moving direction component increases and further away from the currently selected base station, it is opposite to the moving direction direction. In a predetermined angle region including a direction angle, a step of adding a negative correction value set so as to be smaller as the opposite direction component is larger and to be farther away from the currently selected base station; and
And the base station having the maximum received signal strength among the received signal strengths for each base station to which the correction value is added is selected as a base station in the traveling direction of the wireless communication terminal. Item 3. A wireless communication method according to Item 1 or 2.   The radio communication method according to any one of claims 1 to 3, wherein a reception period of a next broadcast information channel burst in the first step is controlled according to the estimated moving speed calculated in the third step. .   The wireless communication method according to claim 4, wherein the reception cycle is controlled to become shorter as the estimated moving speed becomes faster. In a wireless communication terminal that performs wireless communication with a base station using a time division duplex method,
Receiving means for periodically receiving broadcast information channel bursts radiated synchronously from a plurality of base stations;
Relative distance difference calculating means for calculating a relative distance difference for each base station with respect to the wireless communication terminal based on reception timing of sequential broadcast information channel bursts for each base station received by the receiving means;
Based on the relative distance difference for each base station calculated by the relative distance difference calculating means, estimated moving speed calculating means for calculating the estimated moving speed of the wireless communication terminal;
Based on the comparison result between the estimated moving speed calculated by the estimated moving speed calculating means and a predetermined threshold, when the estimated moving speed is equal to or greater than the threshold, each base station calculated by the relative distance difference calculating means Base station selection means for selecting a base station in the traveling direction of movement of the wireless communication terminal based on the relative distance difference;
A wireless communication terminal comprising:

Images